Mike Mills’ “20th Century Women” starts off with a car on fire in a supermarket parking lot. The blazing vehicle in question is a Ford Galaxy that once belonged to the unseen ex-husband of single mother Dorothea Fields (Annette Bening). It’s a fitting opening for a movie that’s steeped in feminism, a striking visual that brings to mind the idea of bra burnings in the ’60s and ’70s.

Apocryphal or not, the symbolism of using one’s brassiere as kindling represents the rejection of the onerous male influence on a woman’s destiny. Therein lies the somewhat paradoxical, if not existential question of the film that writer-director Mills is trying to answer: Does it take a man to raise a man or can a lady find herself equally as capable for the challenge? Unfortunately, it’s an interesting query being pursued by a disappointingly ho-hum movie.

It’s 1979 and Dorothea is doing the best she can with her son Jamie (Lucas Jade Zumann, who exudes all the quiet naivete and good-naturedness of a clueless and hormonal teenage boy) in an idyllic Santa Barbara neighborhood of endless summer. A product of the Great Depression, the 55-year-old, chain-smoking divorcee is a paradox in and of herself. She’s the product of a more puritanical generation who is stuck in her ways (writing down her stock prices every morning and sticking with the same cigarette brand), yet not averse to telling the occasional lie to bust Jamie out of school from time to time.

Fearing that she’s not doing enough for Jamie, Dorothea enlists the help of one of her tenants, cancer survivor Abbie (a red-haired Greta Gerwig) and her son’s best friend, the promiscuous Julie (Elle Fanning), to try and help raise him. That’s where any semblance of a plot begins and ends because “20th Century Women” doesn’t go anywhere.

The movie drops off into a string of boredom-inducing vignettes that have almost nothing significant to say about women’s liberation at the tail end of a truly turbulent decade, at least nothing I could discern, anyway (perhaps I’m just too blinded by the patriarchy). Instead, there’s monotone, omniscient narration while the same stock footage and photos pass across the screen in a tired exercise we’ve seen before. It’s nearly two bloated hours of overblown pretentiousness as if, in some way, Mills set out to make a ’70s-set remake of “American Beauty” with all the aerial shots and Roger Neill’s interesting and synthy score that seems like a callback to the ethereal scores of Thomas Newman.

The movie is at its most honest (and funny) when it’s not trying to teach us something it thinks is profound. When the characters simply don’t give a damn or, you know, just act like regular human beings, things really pop. There’s delightful dinner time conversation about casting off the awkward stigma of a woman’s time of the month and a genuine moment when Dorothea — so steeped in her own upbringing on Louis Armstrong and “Casablanca” (she lovingly refers to Jamie as “kid”) — tries to interpret punk rock and dance to “The Big Country” by Talking Heads like a poorly-oiled robot with her other tenant, an ex-hippie named William (Billy Crudup). Crudup is more wasted potential, looking like his rock star persona from “Almost Famous,” Russell Hammond, was chewed up and spit out by the music industry, a little worse for wear.

While other critics will extol Bening’s heartwarming performance, it’s actually Gerwig and Fanning who steal the show. In particular, this is the second time Fanning has played a teenage heartthrob in movie set in 1979; the first being J.J. Abrams’s PG-13 nostalgia piece “Super 8” back in 2011. However, an R-rating gives her so much more range and freedom as a girl who began sleeping around at the age of 14 and secretly cuddles in the same bed of her best friend who’s also harboring a secret love for her that she won’t reciprocate. Gerwig’s Abbie, on the other hand, inundates Jamie with so much feminist literature that he gets beaten up for trying to explain clitoral stimulation to one of his guy friends who just wants to brag about his one night stand.

Then the cinematography sometimes bursts into multi-colored road trips as if the director of photography was pumping acid into the cameras intravenously during filming. Meanwhile, the sound mixing helps expertly portray the generation gaps, ingeniously comparing the sound of punk music to an electric sander.

It’s stuff like this that shine like beacons on a foggy post-Watergate night, but unlike similar movies set around the same time (“Almost Famous,” “Boogie Nights”), the disjointedness is the real enemy here. There’s some good stuff, but it’s a real chore to sift through the multitude of minutiae. As Jimmy Carter would say, the film, much like the American public in 1979, has a crisis of confidence and a total lack of energy — a little rumination on the oil crisis of the time.

While I (and my own Baby Boomer mother who came of age in the 1970s) didn’t care much for “20th Century Women,” it’s still a relevant piece of cinema about female self-determination that can’t help but mirror the current political and social climate caused by the recent presidential election and subsequent women’s march — enough so to gain Mills an Oscar nod for Best Original Screenplay.

“My son grew up with a needless war, protests and Nixon,” says Dorothea with blatant disdain, obviously talking across the years to modern audiences with the message that some things never change. Once the credits roll and the lights come up, the words of Humphrey Bogart’s Rick Blaine may be ringing in your ears, “It doesn’t take much to see that the problems of three little people don’t amount to a hill of beans in this crazy world. Someday you’ll understand that.” Given the struggles of Mills’ three damaged main characters that are never truly resolved, maybe Rick was talking about Dorothea, Abbie and Julie all along.